The present invention relates to S-parameter measurement systems. It finds particular application in conjunction with measurement systems for measuring transmission and reflection parameters of radio frequency coils of magnetic resonance scanners and will be described with particular reference thereto. It is to be appreciated, however, that the present invention will also be useful for quantifying performance of RF coils and other RF hardware, such as transmission/reception boxes, probe multiplexers, preamplifiers, and the like.
Heretofore, the RF coils of magnetic resonance imaging devices have been measured with a network analyzer in conjunction with an S-parameter test set. A network analyzer is a large, complex piece of laboratory equipment. Its large size and high cost render it undesirable to make it a part of each service technician's repair kit which is carried to the site of an MR imaging system.
When it is necessary to test or check the parameters of the RF coil of an MR imaging system, the coil is commonly interconnected with an S-parameter test set, which, in turn, is interconnected with the network analyzer. The S-parameter test set allows the network analyzer to make transmission and reflection measurements into both forward and reverse directions.
Rather than using an S-parameter test kit, one can use a reflection/transmission kit and a resistive divider. Although the reflection transmission kit and the resistive divider are significantly less costly than an S-parameter test set, the much more expensive network analyzer is still needed. Moreover, although the reflection/transmission kit allows the necessary measurements to be made, the coil must be disconnected and reconnected in different ways to make all of the measurements to determine the S-parameters. To save connecting and reconnecting the coil, one can use a two port measurement instrument in conjunction with the network analyzer.
In order to avoid the weight and the cost of a network analyzer, the S-parameters can be measured using a less expensive spectrum analyzer in conjunction with a directional bridge and a single port device. With this arrangement, it is possible to measure port 1 of a two port coil while port 2 is manually terminated with a 50 Ohm terminator. Port 2 can then be measured by swapping the device under test, making port 2 the input port and port 1 the terminated port. The transmission parameter can be measured by removing the directional bridge and hooking port 1 to the source output on the spectrum analyzer and then hooking port 2 to the receiver input. All of these measurements require moving the coil or other device under test and changing the test setup. The addition of cables and terminations required for some measurements can change the measured parameters and cause inaccurate results. Moreover, this arrangement has no provision for DC bias.
The present invention contemplates a new and improved S-parameter test kit for use in conjunction with a spectrum analyzer which overcomes the above-referenced problems and others.